1. Field of the Invention
The present invention relates to an aqueous coating composition which comprises as one binder component an aqueous polymer dispersion suitable for application as a basecoat to a substrate surface, to a process for producing a multilayer coating, and to the resulting coating. The aqueous polymer dispersion comprises
(i) an acrylate polymer based on from 30 to 60% by weight of C.sub.1 -C.sub.8 -alkyl (meth)acrylate monomers, from 30 to 60% by weight of vinylaromatic monomers and from 0.5 to 10% by weight of (meth)acrylic acid PA0 (ii) a nonassociative rheology stabilizer comprising an acrylate copolymer based on C.sub.1 -C.sub.6 -alkyl (meth)acrylate and (meth)acrylic acid, and PA0 (iii) as crosslinker, tris(alkoxycarbonylamino)-triazine or a mixture of tris(alkoxycarbonylamino)-triazines. PA0 i) an acrylate polymer based on from 30 to 60% by weight of C.sub.1 -C.sub.8 -alkyl (meth)acrylate monomers, from 30 to 60% by weight of vinylaromatic monomers and from 0.5 to 10% by weight of (meth)acrylic acid and PA0 (ii) a nonassociative rheology stabilizer comprising an acrylate copolymer based on C.sub.1 -C.sub.6 -alkyl (meth)acrylate and (meth)acrylic acid, and PA0 (iii) as crosslinker, tris(alkoxycarbonylamino)-triazine or a mixture of tris(alkoxycarbonylamino)-triazines. PA0 i) an acrylate polymer comprising from 30 to 60% by weight of C.sub.1 -C.sub.8 -alkyl (meth)acrylate monomers, from 30 to 60% by weight of vinylaromatic monomers and from 0.5 to 10% by weight of (meth)acrylic acid and PA0 (ii) a nonassociative rheology stabilizer comprising an acrylate copolymer which comprises C.sub.1 -C.sub.6 -alkyl (meth)acrylate and (meth)acrylic acid, and PA0 (iii) as crosslinker, tris(alkoxycarbonylamino)-triazine or a mixture of tris(alkoxycarbonylamino)-triazines. PA0 (A) an aqueous coating formulation which comprises the coating composition described above as film-forming agent is applied as basecoat composition to a substrate surface coated with a customary filler, PA0 (B) a suitable transparent topcoat composition or formulation is applied to the resultant basecoat, and PA0 (C) the basecoat is stoved or baked together with the topcoat. PA0 (D) an aqueous basecoat formulation (Y) which comprises an aqueous polymer dispersion as defined above as film-forming agent is applied to a substrate surface coated with an aqueous basecoat formulation (X), PA0 (E) a suitable transparent topcoat formulation is applied to the formulation obtained in stage (D) and PA0 (F) the basecoat formulations (X) and (Y) are stoved or baked together with the topcoat formulation.
2. Discussion of Relevant Art
The prior art discloses processes for coating vehicle bodies, especially automobile bodies, in which the substrate surface is coated in general first with an electrodeposition coating material and/or antistonechip intermediate primer or a filler coat and then, using a coating material comprising at least one pigment, a pigmented basecoat film is applied and this basecoat film is overcoated, if desired, with a transparent coating material. The single-coat or multicoat finish obtained in this way is subsequently stoved or baked.
The basecoat materials used to produce the basecoat film are usually water-based or solvent-based systems. As principal binders they generally comprise polyurethane dispersions or acrylate dispersions, in combination with water-miscible, crosslinkable polyesters and water-miscible melamine resins, which give rise to a series of problems, examples being low storage stability, tendency to yellow, and unstable viscosity.
For ease of processing and a good and uniform appearance of the coated substrate, the pigmented basecoat materials require a pseudoplastic behavior in combination with a certain non-Newtonian behavior. Ease of processing includes, in particular, good sprayability, storage stability, stirring stability, and stability in a closed pipeline circuit. The appearance of the coated substrate is notable for good coverage of sanding spots, a high metallic effect, good adhesion to the substrate and any further coatings applied thereto, water spray resistance, and weathering stability.
Properties of this kind are particularly advantageous, in the case of metallic finishes, for the development of a high metallic effect.
The pseudoplastic behavior and non-Newtonian behavior should be developed fully by the coating materials in particular from a pH of 6 to about 8 in view of the pH values of the binder solutions employed. In order to obtain such properties, it is common to employ thickeners or Theological assistants such as ionic sheet silicates, xanthan gum, diurea compounds, polyurethane thickeners, bentonite, waxes, and wax copolymers.
However, the use of these thickeners does not lead in every case to the desired coating results, and there may also be problems in the course of processing, i.e., in the course of painting.